1. Field of the Invention
The present invention relates to a ceramic material with a small resistance-temperature coefficient, and, more particularly, to a ceramic material which can be effectively used to serve as the heating element of a self-controlling type glow plug.
2. Description of the Related Art
Hitherto, ceramic heating elements have been prepared by combining and dispersing electrically conductive ceramics such as TiN and MoSi.sub.2 and insulating type ceramics such as Si.sub.3 N.sub.4 and sintering these combined ceramics.
However, a sufficiently reduced resistance temperature coefficient could not be obtained in a ceramic heating element of such a type as described above, because attempts to reduce the resistance-temperature coefficient meet inherent limitations due to usual influence of the specific temperature-resistance coefficient of electrically conductive ceramics such as TiN and MoSi.sub.2.
For example, a known self-controlling type glow plug is provided with the above-described type ceramic heating element and a resistor for controlling electric current connected in series to said element.
Since the resistance-temperature coefficient of the element cannot be sufficiently reduced, the heating element itself acts as the resistor when the temperature of the heating element is raised, the amount of electric current to be supplied to the heating element cannot be controlled properly with the resistor for controlling electric current, and satisfactory temperature-rising characteristics cannot be obtained.